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  <div class="section" id="platform-support">
<span id="asyncio-platform-support"></span><h1>Platform Support<a class="headerlink" href="#platform-support" title="Permalink to this headline">¶</a></h1>
<p>The <a class="reference internal" href="asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O."><code class="xref py py-mod docutils literal notranslate"><span class="pre">asyncio</span></code></a> module is designed to be portable,
but some platforms have subtle differences and limitations
due to the platforms’ underlying architecture and capabilities.</p>
<div class="section" id="all-platforms">
<h2>All Platforms<a class="headerlink" href="#all-platforms" title="Permalink to this headline">¶</a></h2>
<ul class="simple">
<li><p><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_reader" title="asyncio.loop.add_reader"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_reader()</span></code></a> and <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_writer" title="asyncio.loop.add_writer"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_writer()</span></code></a>
cannot be used to monitor file I/O.</p></li>
</ul>
</div>
<div class="section" id="windows">
<h2>Windows<a class="headerlink" href="#windows" title="Permalink to this headline">¶</a></h2>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.8/Lib/asyncio/proactor_events.py">Lib/asyncio/proactor_events.py</a>,
<a class="reference external" href="https://github.com/python/cpython/tree/3.8/Lib/asyncio/windows_events.py">Lib/asyncio/windows_events.py</a>,
<a class="reference external" href="https://github.com/python/cpython/tree/3.8/Lib/asyncio/windows_utils.py">Lib/asyncio/windows_utils.py</a></p>
<hr class="docutils" />
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.8: </span>On Windows, <a class="reference internal" href="asyncio-eventloop.html#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProactorEventLoop</span></code></a> is now the default event loop.</p>
</div>
<p>All event loops on Windows do not support the following methods:</p>
<ul class="simple">
<li><p><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_unix_connection" title="asyncio.loop.create_unix_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_unix_connection()</span></code></a> and
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_unix_server" title="asyncio.loop.create_unix_server"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_unix_server()</span></code></a> are not supported.
The <a class="reference internal" href="socket.html#socket.AF_UNIX" title="socket.AF_UNIX"><code class="xref py py-data docutils literal notranslate"><span class="pre">socket.AF_UNIX</span></code></a> socket family is specific to Unix.</p></li>
<li><p><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_signal_handler" title="asyncio.loop.add_signal_handler"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_signal_handler()</span></code></a> and
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.remove_signal_handler" title="asyncio.loop.remove_signal_handler"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.remove_signal_handler()</span></code></a> are not supported.</p></li>
</ul>
<p><a class="reference internal" href="asyncio-eventloop.html#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorEventLoop</span></code></a> has the following limitations:</p>
<ul class="simple">
<li><p><a class="reference internal" href="selectors.html#selectors.SelectSelector" title="selectors.SelectSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectSelector</span></code></a> is used to wait on socket events:
it supports sockets and is limited to 512 sockets.</p></li>
<li><p><a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_reader" title="asyncio.loop.add_reader"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_reader()</span></code></a> and <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_writer" title="asyncio.loop.add_writer"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_writer()</span></code></a> only accept
socket handles (e.g. pipe file descriptors are not supported).</p></li>
<li><p>Pipes are not supported, so the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.connect_read_pipe" title="asyncio.loop.connect_read_pipe"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.connect_read_pipe()</span></code></a>
and <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.connect_write_pipe" title="asyncio.loop.connect_write_pipe"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.connect_write_pipe()</span></code></a> methods are not implemented.</p></li>
<li><p><a class="reference internal" href="asyncio-subprocess.html#asyncio-subprocess"><span class="std std-ref">Subprocesses</span></a> are not supported, i.e.
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_exec" title="asyncio.loop.subprocess_exec"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_exec()</span></code></a> and <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_shell" title="asyncio.loop.subprocess_shell"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_shell()</span></code></a>
methods are not implemented.</p></li>
</ul>
<p><a class="reference internal" href="asyncio-eventloop.html#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProactorEventLoop</span></code></a> has the following limitations:</p>
<ul class="simple">
<li><p>The <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_reader" title="asyncio.loop.add_reader"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_reader()</span></code></a> and <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_writer" title="asyncio.loop.add_writer"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_writer()</span></code></a>
methods are not supported.</p></li>
</ul>
<p>The resolution of the monotonic clock on Windows is usually around 15.6
msec.  The best resolution is 0.5 msec. The resolution depends on the
hardware (availability of <a class="reference external" href="https://en.wikipedia.org/wiki/High_Precision_Event_Timer">HPET</a>) and on the
Windows configuration.</p>
<div class="section" id="subprocess-support-on-windows">
<span id="asyncio-windows-subprocess"></span><h3>Subprocess Support on Windows<a class="headerlink" href="#subprocess-support-on-windows" title="Permalink to this headline">¶</a></h3>
<p>On Windows, the default event loop <a class="reference internal" href="asyncio-eventloop.html#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProactorEventLoop</span></code></a> supports
subprocesses, whereas <a class="reference internal" href="asyncio-eventloop.html#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorEventLoop</span></code></a> does not.</p>
<p>The <a class="reference internal" href="asyncio-policy.html#asyncio.AbstractEventLoopPolicy.set_child_watcher" title="asyncio.AbstractEventLoopPolicy.set_child_watcher"><code class="xref py py-meth docutils literal notranslate"><span class="pre">policy.set_child_watcher()</span></code></a> function is also
not supported, as <a class="reference internal" href="asyncio-eventloop.html#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProactorEventLoop</span></code></a> has a different mechanism
to watch child processes.</p>
</div>
</div>
<div class="section" id="macos">
<h2>macOS<a class="headerlink" href="#macos" title="Permalink to this headline">¶</a></h2>
<p>Modern macOS versions are fully supported.</p>
<p class="rubric">macOS &lt;= 10.8</p>
<p>On macOS 10.6, 10.7 and 10.8, the default event loop
uses <a class="reference internal" href="selectors.html#selectors.KqueueSelector" title="selectors.KqueueSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">selectors.KqueueSelector</span></code></a>, which does not support
character devices on these versions.  The <a class="reference internal" href="asyncio-eventloop.html#asyncio.SelectorEventLoop" title="asyncio.SelectorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorEventLoop</span></code></a>
can be manually configured to use <a class="reference internal" href="selectors.html#selectors.SelectSelector" title="selectors.SelectSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectSelector</span></code></a>
or <a class="reference internal" href="selectors.html#selectors.PollSelector" title="selectors.PollSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">PollSelector</span></code></a> to support character devices on
these older versions of macOS.  Example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="kn">import</span> <span class="nn">selectors</span>

<span class="n">selector</span> <span class="o">=</span> <span class="n">selectors</span><span class="o">.</span><span class="n">SelectSelector</span><span class="p">()</span>
<span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">SelectorEventLoop</span><span class="p">(</span><span class="n">selector</span><span class="p">)</span>
<span class="n">asyncio</span><span class="o">.</span><span class="n">set_event_loop</span><span class="p">(</span><span class="n">loop</span><span class="p">)</span>
</pre></div>
</div>
</div>
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